In the right context they are all possible. I'd say that (b) is the most natural of the three. Here is how I would probably write your sentence: It's not like they judge based on some objective standard.
New words, one handy idiom, and a 2-minute quiz — delivered to your inbox to keep your streak alive.
seagullis natural, and which is not?The first two are natural. The last one is not.
seagullhow would a native speaker say itI would probably say